The present invention relates generally to mass spectrometry of secondary particles, charged either positively or negatively, which are emitted when solids or liquids absorb energy from primary particles, including photons. More particularly, the invention relates to apparatus for obtaining measurements of secondary ions, in systems which have become known as secondary ion mass spectrometry (SIMS) devices. Such devices have been known generally for a number of years, and continual progress in improving the accuracy and adaptability of such devices has been made over the years. The present invention is yet a further improvement in SIMS devices.
An early patent in the field of SIMS devices is U.S. Pat. No. 3,517,191, issued June 23, 1970 to Liebl. This patent discloses an electrostatic ion energy analyzer followed by a magnetic mass spectrometer. Another early patent, U.S. Pat. No. 2,939,952, issued June 7, 1960, to Paul et al discloses a quadrupole mass spectrometer. A subsequent patent, U.S. Pat. No. 3,939,344, issued Feb. 17, 1976 to McKinney, discloses a SIMS device utilizing a quadrupole mass spectrometer. Subsequently, U.S. Pat. No. 4,132,892 issued Jan. 2, 1979 to Wittmaack, disclosed a raster scanning ion microprobe for determining, with a large field of view, the lateral distribution of elements, isotopes and compounds at the surface and in the bulk of solid specimens for displaying the surface topography of the sample. This device also utilized a quadrupole mass analyzer to allow imaging of the specimen with a large field of view U.S. Pat. No. 4,296,323, issued Oct. 20, 1981 to Gerlach, discloses an improved SIMS device having a focusing ion collection lens, quadrupole mass analyzer, and an electron multiplier-type ion detector. U.S. Pat. No. 4,556,794, issued Dec. 3, 1985 to Ward et al discloses a SIMS device having a secondary ion collection and transport system which is very compact and can be used with a small working distance, thereby enabling the primary ion beam to have a short focal length and high resolution, and collect the secondary ions on the same axis as the primary ion beam. The transport section consisted of a plurality of spaced conductive members which are coaxial with and distributed along the desired ion path, and relatively high voltages were applied to alternate transport sections to produce accelerating electric fields sufficient to transport the ions through the section to an ion mass analyzer, while lower voltages were applied to the other transport sections to focus the ions and bring their velocity to a level compatible with the analyzing apparatus.
U.S. Pat. No. 3,617,741, issued Nov. 2, 1971 to Siegbahn et al discloses an electron spectroscopy system with a multiple electrode electron lens, utilizing a hemispherical plate electrostatic analyzer, specifically for analysis of X-ray induced photoelectrons, but generally of a type able to energy-analyze charged subatomic particles, atomic or molecular particles. U.S. Pat. No. 4,481,415, issued Nov. 6, 1984 to Takeda et al discloses a specific form of quadrupole mass spectrometer, which includes a modification to collimate and focus both low- and high-mass charged particles at the same point on the detector.
The foregoing patents disclose SIMS devices and specific elements for incorporating therein, and represent improvements over similar devices previously disclosed. The present invention likewise includes improvements over prior art devices, the result being an overall improved secondary ion mass spectrometer apparatus.